1. Field of the Invention:
This invention relates to a method of manufacturing high-purity silicon rods, for use in a float zone melting process, by pyrolyzing monosilane on rod-shaped and red-heated silicon carrier members located within a pyrolysis container thereby depositing high-purity silicon thereon, and more particularly to a method of producing high-purity silicon rods having a uniform sectional shape.
2. Description of the Prior Art:
Semi-conductive silicon rods have heretofore been manufactured by pyrolyzing or reducing by hydrogen a gaseous silicon compound, such as monosilane, silicon tetrachloride, trichloro-silane, etc., which has been refined on rod-shaped and red-heated silicon carrier members or a high-melting point metal having good electric conductivity such as, for example, tantalum wire, thereby depositing high-purity silicon on the carrier members. Such methods of manufacturing high-purity silicon rods include the process of blowing off a raw material gas from the lower side disclosed in U.S. Pats. Nos. 3,011,877 and 3,099,534, and the process of blowing off a raw material gas from the upper side disclosed in U.S. Pat No. 3,147,141. In the case of depositing silicon on rod-shaped and red-heated silicon carrier members in the process of blowing off a raw material gas from the lower side, the diameter of the lower part of each silicon rod to be grown up tends to become greater than that of the upper part thereof, and such tendency will become more conspicuous with the increase of the diameter of each silicon rod to be grown up. Further, in the case of depositing silicon on the rod-shaped and red-heated silicon carrier members in the process of blowing off a raw material gas from the upper side, the diameter of the upper part of each silicon rod tends to become greater than that of the lower part thereof, and such tendency will become more conspicuous with the increase of the diameter of each silicon rod to be grown up.
Whilst, the silicon rods used for manufacturing single-crystal silicon by a float zone melting process are usually molded to have a uniform diameter or an approximately perfect roundness by scraping off uneven parts of the silicon rods with a view of preventing occurrence of possible accidents resulting from the irregular shape thereof during the float zone melting process. As mentioned above, silicon rods obtained by the rod-shaped multi-crystal silicon manufacturing process will have imperfect roundness or uneven diameter in the longitudinal direction thereof, and therefore tend to reduce the yield thereof with the increase of the diameter of the raw material for single-crystal silicon.
A part of the above-mentioned disadvantages can be overcome by the method which has already been proposed by the applicant of the present invention; that is, the method of manufacturing silicon rods having approximately perfect roundness by pyrolyzing monosilane on a plurality of rod-shaped silicon carrier members which have been red-heated by directly passing an electric current therethrough thereby depositing high-purity silicon thereon while insulating the radiant heat between the carrier members by a thermal insulator. Although formation of silicon rods having an approximately perfect roundness can be ensured by the above-mentioned method, the unevenness in the diameter of the silicon rods in the longitudinal direction cannot be eliminated.